Perfluoropolyethers are highly regarded in the specialty lubricant field because of their wide liquid ranges, low vapor pressures and high thermal and oxidative stabilities. Because of these properties (many of which are unique to fluorocarbons), they are excellent high performance lubricants, superior base stocks for greases, excellent lubricating oils, and heat transfer fluids. In addition, because of these uniquely outstanding properties, saturated perfluoropolyethers are of current interest as specialty sealants, elastomers and plastics.
A reported reaction of saturated perfluoropolyethers is chain cleavage at the ether linkage by aluminum chloride at elevated temperatures to produce acyl chloride and trichloromethyl terminated polymer fragments. (See Tiers, G. V. D., (1955) J. Amer. Chem. Soc. 77:4837, 6703).
In spite of their unlimited potential, only three perfluoropolyethers are commercially available to date. They are:
(1) Du Pont's Krytox.TM. fluid which is made by polymerizing hexafluoropropylene oxide. PA1 (2) Demnum.TM. fluid, a product of Daikin Industries, is obtained by ring opening polymerization of 2,2,3,3-tetrafluorooxetane using a catalyst with subsequent treatment of the highly fluorinated polyether with fluorine gas to give a perfluorinated product (European Patent Application 148,482). PA1 (3) Montedison's Fomblin Z.TM. and Fomblin Y.TM. fluids which are prepared by photooxidizing tetrafluoroethylene and hexafluoropropylene oxide, respectively, in the presence of oxygen. PA1 In another embodiment, the perfluorinated polyether can have a linear chain structure consisting essentially of a total of at least five repeating units, which includes --YO-- and --Y'O--, wherein Y is CR.sub.1 R.sub.2 CR.sub.3 R.sub.4 and Y' is selected from CR.sub.1 'R.sub.2 'CR.sub.3 'R.sub.4 ', CR.sub.1 'R.sub.2 'CR.sub.3 'R.sub.4 'CR.sub.5 'R.sub.6 ', and CR.sub.1 'R.sub.2 'CR.sub.3 'R.sub.4 'CR.sub.5 ', R.sub.6 'CR.sub.7 'R.sub.8 ', wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.1 ', R.sub.2 ', R.sub.3 ', R.sub.4 ', R.sub.5 ', R.sub.6 ', R.sub.7 ' and R.sub.8 ' in each repeating unit comprises F, perfluoroalkyl of one to twenty carbons or a perfluoroalkyl ether of two to twenty carbons. Alternatively, the number of repeating units can be at least ten, fifteen, twenty-five or fifty.
Several fluorinated polyethers have been previously prepared. See U.S. Pat. No. 3,125,599, and U.S. Pat. No. 3,250,806.
A process has been described for preparing perfluoropolyethers by reaction of a hydrocarbon polyether with elemental fluorine in the presence of a hydrogen fluoride scavenger. See U.S. Pat. No. 4,755,567.